The invention relates to a method and apparatus for the measurement of electric currents and/or voltages in a plurality of current or, respectively, voltage circuits, particularly of the middle frequency current circuits in electromedical interference current therapy, whereby the current or voltage of each circuit is compared with a comparative value.
Current or voltage measurements are relatively unproblematic as long as the peak values are not subject to amplitude fluctuations that are all too slow. If, however, such slow amplitude fluctuations occur, then peak value meters with correspondingly large time constants must be employed so that the amplitude fluctuations do not influence the measurement of peak values. Thereby, the required time constant can be so large that changes in the signal behavior which result particularly from technical errors such as the falling off of electrodes ect. are not registered by the peak value meter. This would have as a result that a large peak value would continue to be indicated although, in the meantime, the current had sunk to a fraction of this peak value or entirely down to zero. In this sense, the same is also true for intentional intensity alterations; if the intensity value were regulated down to a lower value by means of an intensity regulator, then, in this case, too, the peak value display would remain unchanged. An area where these problems are particularly relevant is electromedical interference current therapy. Here, where one is always operating with a plurality of current or, respectively, voltage circuits (for example stereodynamic method according to U.S. Pat. No. 4,023,574), the display of the respective peak value of each circuit is always necessary. For the peak value meter used, however, the time constant must then be very large (at least in the minute range), so that, with a parallel arrangement of the circuits, the amplitude fluctuations of very low frequency (circa 0.01/s) which occur do not falsify the display result. However, in a peak value meter with such large time constants, the disadvantages described will then certainly always occur. A change of the transition resistance electrode to the skin or the complete falling off of an electrode will, therefore, not be displayed. A change of the intensity by means of intensity regulators can also not be controlled.